In practice increased hydrocarbon emissions can be produced in the case of e.g. a spark ignition engine with direct gasoline injection due to leakage of one or more injectors as a result of the fact that fuel drips unchecked from the respective leaky injector into the combustion chamber of its associated cylinder and is not properly combusted there. In particular when the engine is started or immediately when or after the engine is switched off, fuel dripping from the respective leaky injector into the combustion chamber of its associated cylinder can then be discharged completely or partially as unburnt hydrocarbon into the environment via the exhaust and/or induction system of the spark ignition engine. Furthermore, an injector leakage of this kind can lead, during the respective combustion cycle of the spark ignition engine, to the unregulated delivery of fuel into the combustion chamber of that cylinder on which a leaky injector is mounted. Moreover, the starting behavior of the spark ignition engine can be impaired by such an injector leakage, since the fuel delivery control phase is impinged on by a leaky injector with an unknown, uncontrollable fault. Similar difficulties due to injector leakage can also occur with other combustion engines with direct fuel injection such as e.g. diesel engines. In addition to or independently of this, a combustion engine which has one or more injectors for a port injection in its at least one intake manifold can also be affected by this.
Although in practice the increased emissions caused by leakage of an injector can be diagnosed in principle, it has not been possible until now to trace back said emissions causally to a specific fault in a motor vehicle having a combustion engine of said type. In addition a different starting behavior of the respective combustion engine can occur without a repair shop being able to give a satisfactory answer and clearly identify a fault to customers in the event of complaints.